1. Field of the Invention
The present invention relates to an autonomous excavating apparatus for autonomously excavating a surface of the earth or other celestial body.
2. Description of the Background Art
In future unmanned lunar missions, it will be necessary to install a measurement unit, such as a lunar seismometer (i.e., a seismometer for measuring moonquakes), on the lunar surface. The moon has substantially no atmosphere, and undergoes extremes of heat and cold, which is a severe environment for such a measurement unit. On the other hand, the lunar surface is covered with sand-like particles (called “regolith”) having a heat-insulating effect. Thus, if the measurement unit is buried at an excavation depth of about 1 m, the external temperature variations can be suppressed to ease the severity of the environment. Therefore, there is a need for a technique of autonomously burying a measurement unit or the like in regolith without human intervention.
Mizuno, et al., Tohoku University, Japan, proposes an excavating apparatus adapted to rotate, by motors, blades provided on an apparatus body to scrape out regolith lying beneath the apparatus body while introducing the scraped soil inside the apparatus body, and discharge the introduced regolith outside the apparatus body by a bucket elevator, while rotating the blades (the following Non-Patent Document 1). According to this article, it is reported that a prototype apparatus sank down by 126 mm in 120 minutes.
FIG. 12 shows the excavating apparatus proposed by Mizuno, et al., wherein the upper figure is a side view thereof, and the lower figure is a bottom view thereof. Two blades 1002a, 1002b are disposed on respective opposite transverse sides of a space beneath a bottom surface of an apparatus body 1001 having an oval shape in transverse section, and adapted to be driven by respective motors 1003a, 1003b. The two motors 1003a, 1003b are rotationally synchronized to prevent interference between the blades 1002a, 1002b. The two motors are adapted to be rotated in opposite directions so as to cancel out torques thereof to prevent rotation of the apparatus body 1001. According to the rotation of the blades 1002a, 1002b, regolith is introduced inside the apparatus body 1001 through an inlet opening 1005. Then, the introduced regolith is carried upwardly by a bucket elevator 1004, and discharged outside the apparatus body.    [Non-Patent Document 1] “Development of a Robot Prototype for Excavation and Exploration of the Moon and Planet”, 199th Workshop, The Society of Instrument and Control Engineers Tohoku Chapter (Dec. 15, 2001)
However, it is considered that the above excavating apparatus involves the following problems.
(1) Due to the structure employing the bucket elevator to discharge regolith outside the apparatus body, it is unable to excavate regolith to a depth greater than a height dimension of the apparatus body.
(2) Due to the blades arranged to be moved relative to the apparatus body, regolith is likely to block a clearance between the apparatus body and each of the blades to preclude the movement of the blades.
(3) Due to a need for providing a regolith-discharging space (i.e., installation space for the bucket elevator) penetrating through the apparatus body, a loading space for payloads, such as a measurement unit, is narrowed.
(4) It is necessary to provide two mechanisms for the rotation of the blades and the discharge of regolith.
(5) The need for rotating the two blades in opposite directions in order to cancel out torques thereof causes complexity in structure and increase in cost and weight.
(6) Due to incapability to move backwardly within regolith, once starting evacuation, it is unable to redo evacuation.
(7) If an excavated hole is cured, the curved region can avoid exposure to solar light to provide enhanced temperature environment. However, the above excavating apparatus is capable of only excavation in a vertical direction.